Magazine R743

Q & A

Joe HowardJoe Howard is a Group Leaderand Director at the Max PlanckInstitute of Molecular Cell Biologyand Genetics in Dresden. He hasalways been on the move. In hisnative Australia he did his PhD onthe neurobiology of vision; in SanFrancisco he worked on hair cellsand hearing; and in Seattle hedeveloped single-moleculetechniques to study microtubulesand kinesins. He wrote a textbookon the Mechanics of MotorProteins and the Cytoskeleton.Currently he is becominginterested in problems indevelopmental biology.

What turned you on to biologyin the first place? I hatedbiology in school and never tookany classes in it as anundergraduate. I studiedmathematics. But I gotincreasingly worried about thefoundations of mathematics andbecame convinced that our abilityto reason was limited by ourlanguage and our brains: there isno hope of teaching a dogcalculus. I did a PhD inneurobiology, though I neverthought about higher brainfunctions. Back in those days, wewould be beaten by oursupervisors if we even mentionedthe word consciousness, becauseit was considered to beexperimentally intractable andonly madmen worked on it. I hadgreat fun working on vision ininsects

Do you have a favourite paper?Horace Barlow’s 1952 paper oncompound eye design — The sizeof ommatidia in apposition eyes,J. Exp. Biol. 29, 667-674 — had abig influence on me when I was aPhD student. He showed that, foran insect-type eye of a givendiameter, there is an optimal sizeof the facets: if they are too big,then the image is too coarselysampled, but if they are too small,then diffraction becomes aproblem and the spatial resolutionis reduced. Looking at a large

range of eye sizes, he found thatthe observed facet sizes werewithin about a factor of two of hisprediction. It stressed theimportance of asking why.

What is the best advice you’vebeen given? I think that scienceis driven by ideas. Even inexperiments, you first have tohave an idea and then you look tosee if it is true. But you have to belooking, otherwise you probablywon’t see it. Also, ideas help youdevelop new techniques:necessity is indeed themotherhood of invention. And asArthur Eddington advised, neverbelieve an experiment until it’sconfirmed by theory.

What role does theory have inbiology? Funnily enough, when Iwas a PhD student inneurobiology at the AustralianNational University, I had twosupervisors — Simon Laughlin, abiologist, and Allan Snyder, amathematician. In the immediatecommunity that I grew up in, wedeveloped theories to explainbiological phenomena and we didexperiments to test theories. Ithought biology was like that. Butit took 20 years before thisapproach diffused out ofneurobiology and entered into themainstream of biology — classicalmolecular and developmentalbiology, for example — and it maynot even be there yet.

Do you have a scientific hero?Hermann Helmholtz. He mademajor contributions to many areasof science. Among other things,he derived the law ofconservation of energy,introduced the concept of thepotential, measured the speed ofthe action potential in frog nerve,invented the ophthalmoscope,worked out how a violin string isexcited by the bow, and wrotetwo very influential books —Physiological Optics and On theSensations of Tone. Helmholtzepitomized science in the 19th

century, where one could dotheory and experiment on one’sown or with a small lab. 20th

century physics went big, and itlooks like 21st century biology isgoing the same way.

Why the interest indevelopmental biology? I thinkthat developmental biology is theheart of biology. It is the mostintractable to chemical andphysical approaches. That makesit most interesting andchallenging. Developmentalbiology means the creation ofform. And obviously mechanicalprocesses play central roles ineverything from cell division togastrulation. But it has been verydifficult to incorporate mechanicalthinking into development, andthis is why Turing ignoredmechanics in his seminal work onreaction-diffusion mechanisms:The chemical basis ofmorphogenesis, Proc. Roy. Soc.B. 237, 37-72, 1952.

But things have changed. Wenow have a very good molecularunderstanding of motor proteinsand the mechanics of thecytoskeleton, and we know whatforce means at the single-molecule level. I think this newunderstanding will be asimportant for cell anddevelopmental biology asHodgkin and Huxley’s work on ionchannels and the action potentialwas for neurobiology: it will putcell mechanics on a firmmolecular footing.

The time is right fordevelopmental biophysics. Wecan build molecule-based modelsfor moving cells and tissues,solve them with the newtechniques of non-linear analysis,and test them with measurementsusing advanced microscopy andimaging processing that allow usto see single molecules insidecells.

What do you think physics-based approaches might tell usabout development? I think thatmitosis is tractable. The key willbe understanding howmechanical communicationbetween the molecules regulatesand coordinates the spindle. Thenthere is the cell cortex and itscontribution to cell shape: this willbe the key to understanding howcell shape changes drive tissuemorphogenesis. I am intrigued bythe possibility that there may beglobal mechanical signals that tellan organ about its overall shape.

But is quantification possible? Iam very encouraged by thereproducibility of developmentalevents. For example, very earlydevelopment of the worminvolves surprisingly complexmorphological movements, yetthey are precisely repeated fromone embryo to the next. This maybe obvious to a developmentalbiologist: if you don’t geteverything right at the beginning,what hope do you have ofbuilding an entire worm? But it isa pleasant surprise for abiophysicist, because it makesgood measurements possible.

Why have you chosen to workin Germany? It was a greatopportunity to be part ofsomething new — a mix of cellbiologists, biophysicists anddevelopmental biologists. InDresden I have great colleaguesand wonderful support from theMax Planck Society.

What is your greatest researchambition? I would like tounderstand the shapes of cellsand tissues.

What do you think are the bigquestions to be answered nextin your field? The biggestchallenge is to simplify biology.There are too many proteins,genes, interactions.... and toolittle understanding.

Any strong views on journalsand the peer review system? Ithink that the peer review systemhas broken down, as evidencedby the amount of rubbish that ispublished. In my view, publishingshould primarily be done by thelearned societies, though privatecompanies can make valuablecontributions such as that madeto production quality byRockefeller Press. The obsessionwith ‘high-impact’ journals is adisease — the important thing isto write good papers. And peopleshould write more books.

Max Planck Institute of Molecular CellBiology and Genetics,Pfotenhauerstrasse 108, 01307Dresden, Germany.E-mail: howard@mpi-cbg.de

Current Biology Vol 15 No 18R744

Quick guide

Mass extinctionsSimon Conway Morris

What are they? Ever beendenied tenure, had a paperrejected by Current Biology, oreven N*****e? This is much, muchworse: death on a big scale,ecologies shot to pieces and aplanet in turmoil. No accident thatthe ‘Big Five’ of mass extinctions(end-Ordovician (445 million years(Ma) ago, late Devonian (375 Ma),end-Permian (251 Ma), lateTriassic (205 Ma) and mostfamously, the K/T (Cretaceous-Tertiary, 65 Ma)) are at or close tomajor stratigraphic boundaries.So biodiversity plunges, but therates and durations of theextinctions are variable, andnearly always there is markedtaxonomic selectivity. Somegroups are hammered, but othersdon’t seem to notice there is amass extinction going on.

Dozing trilobites? It iscustomary to distinguish times ofmass extinction as against theongoing ‘normal’ times ofbackground extinction. Along withthe ‘Big Five’ there are, however,quite a number of minorextinction events. Nevertheless,with the latter there is a growingsuspicion that confoundingfactors, such as volume ofavailable sedimentary rock,influence or even distort diversitycurves. Many species certainlywent extinct when times gotnasty, but perhaps the majoritywent to the wall quietly, but in theface of relentless competitiveattrition. So those icons ofpalaeontology, the trilobites, wereindeed a victim of the mother ofmass extinctions, the end-Permian event, but they werealready well on the way out.

When Gaia calls in sick. PlanetEarth has its ups and downs:global warmings, stupendous ice-ages, mega-eruptions, but by andlarge the biosphere seems tocruise along. But not at the end of

the Permian; here is a planet indeep trouble, with possibly 96%of all marine species becomingextinct. The cause for this haslong remained elusive, but it isnow looking as if two factors wereresponsible. First, the oceans ranout of oxygen, possibly withhighly toxic H2S spilling into theatmosphere. Second, there weretruly massive episodes of floodvolcanism, notably in Siberia. So,from that source add sulphateaerosols and maybe toxicorganohalogens, and the scene isset for millions of years of misery.

Revenge of the microbes. Thedust settles, the biospherestaggers to its feet (metaphoricalor otherwise), and amidst thedebris life restarts, or does it?Well, no. In many cases, therecovery rates are glacially slow.Following the end-Permiandebacle, for example, marinecommunities remained in a stateof shock for up to 8 Ma. Not onlythat, but with the metazoans awaythe microbes will play. Eerily, inpost-extinction times the planetspins back into a Precambrianecology, with widespreadevidence for stromatolites andother signs of microbialresurgence. Actually these so-called anachronistic biota are aforetaste of what will happen inabout a billion years (Ba) whenthe sun swells and the biospherebegins to shut down, forever.

Goodness me, was that animpact? Try speaking about thedeath of dinosaurs without alsomentioning the litany of iridium,shocked quartz, fireball layersand tektites. The K/T event is thetype example of what happenswhen a bolide doesn’t miss. Buthere’s a funny thing. No othermass extinction can be readilylinked to an impact, be it asteroidor comet. Impacts are known, yetseemingly they have little effect.Well, the K/T asteroid was big andground zero was rich in themineral anhydrite (CaSO4), soperhaps massive injection ofsulphate aerosols into theatmosphere tipped the balance.

The bolide misses and thedinosaurs go home for tea…